A dual interface (DI or DIF) smart card (or chip card) is an example of an RFID device, which is a type of secure document, and may generally comprise: an antenna module AM, a card body CB, and a booster antenna BA.
The antenna module AM may generally comprise an RFID chip (bare, unpackaged silicon die) or chip module (a die with leadframe, carrier or the like)—either of which may be referred to as “CM”—mounted to a module tape MT. A module antenna MA may be disposed on the module tape MT for implementing a contactless interface. Contact pads CP (typically six or eight contact pads) may be disposed on the module tape MT for implementing the contact interface. The module tape MT may comprise a pattern of interconnects (conductive traces and pads) to which the chip CM and contact pads CP may be connected. The antenna module (AM) may measure approximately 12×13 mm (for an 8-pad module) or approximately 8×11 mm (for a 6-pad module).
The module antenna MA may be connected, indirectly, via some of the interconnects to the chip CM, or may be directly connected to bond pads BP on the chip CM. The module antenna MA may comprise several turns of wire, such as 112 micron diameter insulated wire. Reference may be made to U.S. Pat. No. 6,378,774 (2002, Toppan), for example FIGS. 12A, B thereof.
The card body CB—which may be referred to as a substrate, or an inlay substrate—may generally comprise one or more layers of material such as Polyvinyl Chloride (PVC), Polycarbonate (PC), PET-G (Polyethylene Terephtalate Glycol-modified), Copolyester (Tritan), Teslin™, synthetic paper, paper and the like. When “inlay substrate” is referred to herein, it should be taken to include “card body”, and vice versa, as well as any other substrate for a secure document, unless explicitly otherwise stated.
The card body CB may be generally rectangular, measuring approximately 54 mm×86 mm (refer to ISO/IEC 7810), having a thickness of approximately 300 μm thick. The card body CB is typically significantly (such as 20 times) larger than the antenna module AM.
The booster antenna BA may generally comprise a relatively large winding which may be referred to as a card antenna CA component (or portion) having a number of turns disposed in a peripheral area of the card body CB, and a relatively small coupler coil (or coupler antenna) CC component (or portion) having a number of turns disposed at a coupling area of the card body CB corresponding to a location of the antenna module AM, and an extension antenna EA component disposed in an upper portion of the card body CB (avoiding an embossing area in a lower portion of the card body CB). The booster antenna BA (and its various components) may comprise wire mounted to (embedded in) the card body CB using an ultrasonic tool comprising a sonotrode and a capillary. See, for example U.S. Pat. Nos. 6,698,089 and 6,233,818. The wire may be non-insulated, insulated, or self-bonding wire, having an exemplary diameter in the range of approximately 50-112 μm.
Nanowires & Nanotubes
When used herein, references to “nanoparticles” should be taken to include nanowires and nanotubes. Any of these may be referred to as “nanostructures”.
A nanowire (NW) is a nanostructure, with the diameter of the order of a nanometer. Alternatively, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less and an unconstrained length. At these scales, quantum mechanical effects are important—which coined the term “quantum wires”. Many different types of nanowires exist, including metallic (e.g., Ni, Pt, Au), semiconducting (e.g., Si, InP, GaN, etc.), and insulating (e.g., SiO2, TiO2). Molecular nanowires are composed of repeating molecular units and are either organic (e.g. DNA) or inorganic (e.g. Mo6S9-xIx). Typical nanowires exhibit aspect ratios (length-to-width ratio) of 1000 or more. As such they are often referred to as one-dimensional (1-D) materials. Nanowires have many interesting properties that are not seen in bulk or 3-D materials. This is because electrons in nanowires are quantum confined laterally and thus occupy energy levels that are different from the traditional continuum of energy levels or bands found in bulk materials. The conductivity of a nanowire is expected to be much less than that of the corresponding bulk material. This is due to a variety of reasons. First, there is scattering from the wire boundaries, when the wire width is below the free electron mean free path of the bulk material. In copper, for example, the mean free path is 40 nm. Nanowires less than 40 nm wide will shorten the mean free path to the wire width. Nanowires also show other peculiar electrical properties due to their size. Unlike carbon nanotubes, whose motion of electrons can fall under the regime of ballistic transport (meaning the electrons can travel freely from one electrode to the other), nanowire conductivity is strongly influenced by edge effects. The edge effects come from atoms that lay at the nanowire surface and are not fully bonded to neighboring atoms like the atoms within the bulk of the nanowire. The unbonded atoms are often a source of defects within the nanowire, and may cause the nanowire to conduct electricity more poorly than the bulk material. As a nanowire shrinks in size, the surface atoms become more numerous compared to the atoms within the nanowire, and edge effects become more important.
High frequency (HF) antennas (13.56 MHz) may include a plurality of nanowire heterostructures, such as core memory, inductive coils made of nanowires, antitheft devices based on nanowire structures, creating RFID tags on paper money to offset fraud.
Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material. These cylindrical carbon molecules have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology. In particular, owing to their extraordinary thermal conductivity and mechanical and electrical properties, carbon nanotubes may find applications as additives to various structural materials.
Nanotubes are members of the fullerene structural family, which also includes spherical buckyballs, and the ends of a nanotube may be capped with a hemisphere of the buckyball structure. Their name is derived from their long, hollow structure with the walls formed by one-atom-thick sheets of carbon, called graphene. These sheets are rolled at specific and discrete (“chiral”) angles, and the combination of the rolling angle and radius decides the nanotube properties; for example, whether the individual nanotube shell is a metal or semiconductor. Nanotubes are categorized as single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). Individual nanotubes naturally align themselves into “ropes” held together by van der Waals forces. Because of the symmetry and unique electronic structure of graphene, the structure of a nanotube strongly affects its electrical properties. For a given (n,m) nanotube, if n=m, the nanotube is metallic; if n−m is a multiple of 3, then the nanotube is semiconducting with a very small band gap, otherwise the nanotube is a moderate semiconductor. Thus all armchair (n=m) nanotubes are metallic, and nanotubes (6,4), (9,1), etc. are semiconducting. In theory, metallic nanotubes can carry an electric current density of 4×109 A/cm2, which is more than 1,000 times greater than those of metals such as copper, where for copper interconnects current densities are limited by electromigration.
US 20120055013 (Finn; 2012) discloses microstructures such as connection areas, contact pads, antennas, coils, plates for capacitors and the like may be formed using nanostructures such as nanoparticles, nanowires and nanotubes. A laser may be used to assist in the process of microstructure formation, and may also be used to form other features on a substrate such as recesses or channels for receiving the microstructures. A smart mobile phone sticker (MPS) mounted to a cell phone with a self-sticking shielding element comprising a core layer having ferrite particles.
Magnetic Materials
A layer of magnetic material having magnetic particles may be supplied in sheet form. The composition of the magnetic sheet may be a layer of PET (polyethylene terephthalate) coated with magnetic particles having a mean size of approximately 10-100 μm (microns). Reference is made to TDK flexible composite electromagnetic sheet materials for improving communication performance in an RFID tag close to a metal case. The topography and dimensions of such magnetic particles can be dimensionally analyzed using a scanning electron microscope (SEM), and their chemical characteristics can be ascertained using an energy dispersive X-ray (EDX) spectrometer. Core layers of reinforcing and support material used in the production of magnetic sheets, such as PET, cannot readily be laminated to form a composite layer with the standard materials used in plastic cards and tags, such as PVC (polyvinylchloride) or PC (polycarbonate), and may typically require the addition of an adhesive layer.
Stainless Steel
Stainless steel, also known as inox steel, is a steel alloy with a minimum of 10.5% chromium content by mass. Stainless steel differs from carbon steel by the amount of chromium present. Unprotected carbon steel rusts readily when exposed to air and moisture.
Stainless steel may be used as a layer in smart cards (or RFID tags, and the like), and may also be used in telephone casings (and the like) to which an RFID tag (or the like) may be mounted.
Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion by blocking oxygen diffusion to the steel surface and blocks corrosion from spreading into the metal's internal structure and, due to the similar size of the steel and oxide ions, they bond very strongly and remain attached to the surface.
Stainless steel is a relatively poor conductor of electricity, exhibiting only a few percent of the electrical conductivity of copper.
Ferritic and martensitic stainless steels are magnetic. Austenitic stainless steels are non-magnetic.
There are different types of stainless steels: when nickel is added, for instance, the austenite structure of iron is stabilized. This crystal structure makes such steels virtually non-magnetic and less brittle at low temperatures. For greater hardness and strength, more carbon is added.
Stainless steels are also classified by their crystalline structure:                Austenitic, or 200 and 300 series, stainless steels have an austenitic crystalline structure, which is a face-centered cubic crystal structure. Austenite steels make up over 70% of total stainless steel production. They contain a maximum of 0.15% carbon, a minimum of 16% chromium and sufficient nickel and/or manganese to retain an austenitic structure at all temperatures from the cryogenic region to the melting point of the alloy.        Ferritic stainless steels generally have better engineering properties than austenitic grades, but have reduced corrosion resistance, because of the lower chromium and nickel content.        Martensitic stainless steels are not as corrosion-resistant as the other two classes but are extremely strong and tough, as well as highly machinable, and can be hardened by heat treatment. Martensitic stainless steel contains chromium (12-14%), molybdenum (0.2-1%), nickel (less than 2%), and carbon (about 0.1-1%), giving it more hardness but making the material a bit more brittle. It is quenched and magnetic.        Duplex stainless steels have a mixed microstructure of austenite and ferrite.        
Other pure metals and alloys are also applicable in the applications cited, their composition will determine the performance of the magnetic shield.
Some Patent References
    EP 0754985 discloses a developing system having a housing (15) used to apply ink to the drum containing magnetic and pneumatic units (4, 5), for touching up the image. Inking of the drum (1) is achieved by applying a wave of solid particles of a pulverized pigment contained in the housing (15) using an ink deposit system. The ink wave moves in the opposite direction to that of the drum (1). The ink deposit system includes a magnetic drum (2) associated with a deflector (3) which is inclined with respect to set horizontal axis. The drum (2) rotates, in the opposite direction to the drum (1) at a set speed. The deflector (3) is arranged in front of a vertical line joining the centers of the drums (1, 2) by an adjustable amount.            Claim 1 of EP 0754985 refers to an inking device of a development drum comprising in an inking container (15) an inking function of the drum, a magnetic retouching function (4), a pneumatic retouching device (11) and a sealing device (12, 13) of the inking container (15) characterized in that the inking of the printing medium drum (1) is carried out by a wave of solid particles containing a magnetic pulverulent pigment contained in the inking container (15) raised by means (2, 3) of the inking device, the said wave displacing in the opposite direction to the displacement of the surface of the printing medium drum (1).            U.S. Pat. No. 7,481,884 discloses an apparatus and method for applying powder coatings to a substrate either directly or by intermediate transfer using a magnetic brush developer.    U.S. Pat. No. 7,615,256 discloses a process for mixing and gentle transport and transfer of powders to substrates.    U.S. Pat. No. 7,799,147 discloses a flaky soft magnetic metal powder and magnetic core member for RFID antenna. The performance index μ′×Q of a magnetic core member, in which a Fe—Si—Cr alloy is used, is further improved. A flaky soft magnetic metal powder, which is used in a magnetic core member for an RFID antenna comprising the above flaky soft magnetic metal powder and a binder, wherein it is composed of an Fe—Si—Cr alloy having an Ms (saturation magnetization)/Hc (coercive force) of 0.8 to 1.5 (mT/Am−1) in an applied magnetic field of 398 kA/m. It is preferable that the flaky soft magnetic metal powder consists of 7 to 23 at % of Si, 15 at % or less of Cr (excluding 0), and the balance being Fe and inevitable impurities, and that it has a weight-average particle size D50 of 5 to 30 μm and an average thickness of 0.1 to 1 μm.    U.S. Pat. No. 7,922,787 discloses methods for the solution-based production of silver nanowires by adaptation of the polyol process.    U.S. Pat. No. 7,537,874 discloses a toner having a high strength magnetite in an amount of from about 10 to about 40 weight percent, wherein the magnetite includes a material selected from the group consisting of FeO, Fe2O3, Fe3O4, gamma iron oxides, cobalt-gamma iron oxides, and mixtures thereof, and further including a developer having a carrier and toner as just described. It also discloses 4-40 micron total toner size to enable electrostatic movement, 77-150 micron magnetite good as carrier particles for magnetic brush.
The following patents may also be of interest:                U.S. Pat. No. 6,345,882 2002 Feb. 12 (Brechat; Nipson) Magnetographic printing process        U.S. Pat. No. 6,120,142 2000 Sep. 19 (Eltgen et al.; Nipson) High-speed printer and the uses of such a printer        U.S. Pat. No. 5,992,323 1999 Nov. 30 (Eltgen; Nipson) Printing process employing removable erasable image portions        U.S. Pat. No. 5,644,987 1997 Jul. 8 (Eltgen; Nipson) Process and apparatus for printing using a magnetic toner which is electrostatically charged        U.S. Pat. No. 5,610,633 1997 Mar. 11 (Eltgen; Nipson) Agent for magnetographic printers and use of such an agent        